Colorado shooting suspect James Holmes may have planned to lure police into his booby-trapped home by playing loud music to attract a noise investigation.Holmes, who killed 12 people during a screening of the new “Batman” film in Aurora, Colorado, is understood to have set a timer to play the same song over and over again in his apartment.

A law enforcement source told the Reuters news agency that it appeared to be an attempt to draw a complaint from neighbours, in the the hope that they might then call police who would try to force their way in.

Chris Henderson, Aurora’s deputy fire chief, said Holmes’ living room was found rigged with trip wires connected to what appeared to be plastic bottles containing an unknown liquid.

The law enforcement source said: “If he was shot and killed, it is without a doubt that these … booby traps were there to murder and inflict casualties upon first responders.”

Kaitlyn Fonzi, a graduate student at University Hospital, who lives in the apartment below, said she heard loud music coming from Holmes’s apartment. She went upstairs and put her hand on the door handle and noticed that it was unlocked, but had no idea of Holmes was present or not was decided not to confront him.

Ms called police, who told her they were busy the shooting and did not have time to respond to a noise disturbance. She said she was shaken to learn later that the apartment was booby trapped.

“I’m concerned if I had opened the door, I would have set it off,” she said.

Dan Oates, Aurora’s chief of police, said that authorities had determined that the apartment was too dangerous for officers to enter and would send a robot in on Saturday to detonate the explosives.

With Holmes in jail and awaiting an initial court appearance on Monday morning, police have declined to reveal what he has told investigators and would not discuss possible motives for Thursday night’s shooting rampage.

Late on Friday night, police went door to door with a list of those who died in the shooting, notifying families who had held out hope that their loved ones had been spared.

Among the victims was 23-year-old Micayla Medek, disclosed Anita Busch, the cousin of her father.

Knowing her fate after waiting without word brought them some peace, she said, adding: “I hope this evil act, that this evil man doesn’t shake people’s faith in God.”